1. Field of the Invention
The present invention relates to an optical lens, more particularly to a zoom projection lens for projector.
2. Description of the Related Art
In recent years, a Cathode Ray Tube (CRT) projector has been gradually replaced by a Liquid Crystal Display (LCD) projector, a Digital Light Processing (DLP) projector, and other relatively compact projectors.
Accordingly, in a non-telecentric system of the DLP projector, a chief ray is unparallel to an optical axis. A total internal reflection prism may be omitted in a zoom projection lens of the non-telecentric system, compared with a zoom projection lens of a telecentric system, so as to save cost of the zoom projection lens. Moreover, since the chief ray is unparallel to the optical axis in the non-telecentric system, the chief ray enters the zoom projection lens at a nonzero angle with reference to the optical axis. Therefore, a position of a projected image is deviated upwardly, so as to satisfy a requirement of a front-projector.
A conventional front projector with a non-telecentric system is disclosed in Taiwanese Patent No. I288290, which includes a first lens set and a second lens set. The first lens set includes four lenses, and the second lens set includes seven lenses. Owing to a relatively great number of lenses, a cost of the conventional front projector may not be effectively saved, and a length of a zoom projection lens of the conventional front projector may not be reduced such that a need for compact design may not be satisfied.